Cat 988F Braking issue

[988Driver]

Hi all,

Just after some ideas in regards to a braking issue on my 988F. If the brake is held on for a short period of time I am finding that the warning horn goes off and the park brake applies itself. I’m sure there would be a leak in the system somewhere, either the valve group or accumulator group.

Wondering if anyone has had any trouble with this and any pointers on a plan of attack. Is it normally just a matter of resealing either the valve group or accumulator group?

Cheers everyone, keen to hear your thoughts.

 

[Jonas302]

Defiantly look to resealing and charging the accumulators they should go a certain number of pumps after the engine is shut down before the light comes on If they have never been charged you may just get away with that If when you hook the gauges up oil comes out of the port that the nitrogen goes in it for sure needs a reseal

 

[Nige]

If the brake is held on for a short period of time I am finding that the warning horn goes off and the park brake applies itself.

Most likely cause is a leaking brake piston seal (or more than one) in a wheel group.
You have four corners to choose from. Testing by blanking off the brake line to the front axle (easier to get at because it goes across the articulation hitch) and see if the symptoms persist. If they do then you have to blank first one rear brake, then the other, to identify the culprit.
After doing that it's worth while to blank the line to the rear axle and test the front brakes the same way as above just to make sure you don't have a leaker there as well. If you find more than one corner leaking it might pay you to reseal the brake pistons in all four wheels.

You don't say whether you have a Series I (8YG) or a Series II (2ZR) machine. The service brake lines are not completely identical between the two models.

Rough & ready check of the accumulator precharge, start the engine and give the brake pump time to charge up the accumulator(s). Stop the engine, turn the key back on again, and allow a few seconds for the panel to self-test. Fully depress the brake pedal and immediately release it. How many times can you do that before the low pressure warning comes on.?

By "valve group" I assume you mean the brake treadle valve.? This would probably be the last item on the list but if the problem is the same (warning buzzer and park brake applied if the pedal is depressed for a while) whether you use the left pedal or the right brake pedal then it is highly unlikely the treadle valves are the cause.

 

[heymccall]

Simply check both axle oil levels. The over full one has a bad brake piston seal.

 

[kshansen]

Simply check both axle oil levels. The over full one has a bad brake piston seal.

I'm a bit slow getting around to reading this, so yes that is one obvious sign!

I was a bit disappointed on a smaller Cat that had this problem that after I diagnosed the problem that they decided to farm out the job and not bring it to the shop at the quarry for me to handle. This particular machine was one that has the inboard mounted brakes, brakes are near the differential and the axle shafts connect from the brake to the wheels!

Looked like a fun project!

 

[John C.]

In board brakes are great for the operation of the machine. They aren't so fun when it comes time to remove the axle in order to repair them. I've never had access to big powered jacks and lots of fancy over head lifts when I had to work on those machines. The rear axles are a real pain!

 

[Nige]

In board brakes are great for the operation of the machine. They aren't so fun when it comes time to remove the axle in order to repair them.

Removing a wheel end (as in this case) is much easier.

 

[kshansen]

Removing a wheel end (as in this case) is much easier.

Had to do a few 988 87A brake jobs with the help of a tire changing boom truck. That was a fun job!

If the loader with the inboard brakes had come to our shop we had a 40 ton overhead crane to handle the lifting and a good assortment of wood blocking and some good but not MSHA approved jack stands. Along with a few smaller swing boom cranes down the side of the shop.

Just did a search of old files I saved and found that the loader I was talking about was a 970F.